The present invention relates to mobile radio communications systems and, in particular, to a novel method and mobile radio communications unit for more convenient initiation of calls and for increasing the effective use of communication channels assigned for mobile telephone service.
Approximately twelve communication channels, each including two distinct frequencies for two-way communications (an up-link and a down-link), are typically available for use in present day mobile telephone systems. In one known system, usually referred to as Improved Mobile Telephone Service (IMTS), communication is established over the available channels from a wire line telephone system to mobile units through the use of transmitters which transmit omnidirectionally throughout a large geographical area or zone from an antenna approximately centered in the area. A plurality of satellite receivers are spaced throughout the geographical area to receive transmissions from the mobile units and relay the transmissions to the central location. Calls are established through seizure of a marked idle channel by a mobile unit and by placing or receiving a call over the seized marked idle channel.
With only twelve channels available for use in this type of system, only twelve simultaneous conversations are possible and, not only is the total number of subscribers in a service area necessarily limited, but also the subscribers who do obtain service tend to find circuits busy a very high percentage of the time when attempting to place a call. It can thus be seen that 12-channel systems based upon large zone coverage from a central location have been unable to meet present user demands, let alone future requirements for mobile radiotelephone service.
It has been proposed that a large number of channels in about the 900 MHz. band be allocated for mobile telephone use. This increase in the number of available channels will, of course, result in an increase in the number of users that the system is capable of serving. However, known systems do not lend themselves to the effective use of this larger channel allocation particularly in view of the signaling approaches employed. Moreover, known systems do not provide the degree of flexibility which will eventually be desired in mobile telephone systems having a large number of subscribers who are, to at least some extent, free to move over relatively long distances within and/or between one or more distinct mobile telephone systems.
The mobile telephone units utilized with known radiotelephone systems present other unique problems both in IMTS applications and more advanced systems designed for larger channel allocation. For example, present user dialing procedures and IMTS signaling methods are relatively inefficient and waste considerable air time. Each call from the mobile unit in a mobile telephone system requires transmitting the user's Automatic Number (identification) (hereinafter ANI), consisting of 7 digits, and the called number, which may be 7 or 10 digits. The time required to transmit 17 digits using conventional IMTS tone signaling techniques is on the order of 20 seconds. Although the user is billed for this time, the net effect is a loss of revenue to the operating companies, increased billing costs to the subscriber and considerable customer dissatisfaction with the service provided.
Moreover, mobile telephone units are typically installed in automobiles or other such vehicles and the operators' attention must ordinarily be directed primarily to the operation of the vehicle. With known mobile telephone units, the unit scans the available spectrum for an idle channel and locks onto the idle channel if one is so designated. The telephone handset must be lifted from the hook-switch to place a call and, when the handset is lifted, the unit may be either scanning or locked onto the idle channel. If the unit is scanning, the scanning stops and no dial tone is present. The user must therefore hang up and try again. If a dial tone is present signifying that the unit is locked onto an idle channel, the idle channel is seized and the user must then dial the desired number.
It is, of course, quite inconvenient and may be dangerous to place a call in this manner if the vehicle is in motion. Known approaches to initiating and establishing a call are additionally time consuming and require considerable effort on the part of the mobile telephone unit operator. Moreover, from the time the idle channel is seized until the call has been completed, that channel is unavailable for use by others. Since this time period includes dialing time and perhaps other wasted time, the overall use of the available channels is inefficient. Also, experience indicates that misdialing, in a vehicular environment, is a frequent occurrence, which results in additional loss of air time and higher cost to the user.
It is accordingly an object of the present invention to provide a novel method and mobile communication unit for increasing the effective use of available communication channels.
It is an object of the present invention to provide a novel method and mobile communication unit for more effectively employing a large number of communication channels allocated to the system.
It is a further object of the present invention to provide a novel method and mobile telephone unit for establishing and maintaining mobile telephone communications through one or more base stations in predetermined zones of a service area.
It is another object of the present invention to provide a novel method and mobile telephone unit in which a designated control channel is employed for initial call-up signaling to and from the mobile unit and for talking channel assignment.
It is still another object of the present invention to provide a novel method and mobile telephone unit operable in conjunction both with advanced signaling techniques and with known techniques.
It is still a further object of the present invention to provide a novel mobile telephone supervisory control sequencer and method for simplified placement and reception of calls by the mobile unit operator.
These and other objects and advantages are accomplished in accordance with the present invention as will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description and claims when read in conjunction with the drawings.